In Japan, along with aging of the society, over 4 million patients with dementia are imposing increasingly heavy financial and psychological burdens on the entire society. Although there is no medical treatment capable of completely curing dementia so far, early detection of dementia has a potential to slow down progression of dementia by a pharmacological method and appropriate medical care, thereby contributing to significant reduction in health-care cost.
While estimation of an activity in a deep brain region has been conventionally carried out using a PET method, an fMRI method, an MEG method or the like, these methods still involve usability problems and a problem of a need for a large-scale apparatus. In this situation, electroencephalography (EEG) for observing a brain potential (electrical potential) monitored on the scalp (scalp potential) has been widely used in clinical sites because it does not require any large-scale apparatus. In the International 10-20 system used in a standard clinical examination, from a standpoint of, in clinical sites, monitoring a potential distribution on the scalp by a large number of electrodes, potentials have been monitored using 19 electrodes, and recorded in a pen recorder or a hard disk drive in a computer.
As a specific method, there has been developed a system configured to, assuming that a brain potential monitored on the scalp is generated by an equivalent dipole power source assumedly located inside the brain, equivalently express the brain potential by a “dipole tracing method” for inversely estimating a position, direction and current value of the equivalent dipole power source from a brain potential distribution on the scalp (the following Non-patent Document 1). In this system, because both a thalamus acting as part of a source of an α wave and a hypothalamus which is a major part of expression of emotion are located in a brainstem region adjacent to a center of the brain, the technique of assuming an equivalent dipole power source in a deep brain region has been considered to be effective in evaluating activities thereof. As used herein, the term “deep brain region” means a site indicative of a brainstem region and a cerebral limbic system around the brainstem region.
There has also been developed a system (a DIMENSION system) configured to express, by an index, called “dipolarity (Dα)”, a degree of accuracy with which the inversely-estimated dipole power source can express a scalp potential. This index is intended to quantitatively analyze a dipole potential activity to estimate an activity of a deep brain region, and largely varies depending on a stage of dementia, so that it has been used as a means to detect dementia (the following Non-Patent Documents 2 and 3).
Further, as a different approach from the above, there has been developed a brain activity measurement device intended to three-dimensionally identify an abnormal site in terms of neuronal activity (the following Patent Document 1).